1. Field of the Invention
The present invention relates to an electrodeless electrolytic dressing grinding method and apparatus capable of grinding a workpiece and dressing the working surface of a grindstone simultaneously.
2. Description of the Related Art
Problems in the finishing process of a mold having a free form surface include a low degree of freedom of shape in the copying process with a grindstone and a necessary correction of the grindstone. Profile processing with a straight grindstone is restricted as to profiling shape due to the low degree of freedom of the diameter and the tip radius of the grindstone and a process machine itself. Further, the problems of a blade-like (thin blade) grindstone are that a working surface like a point causes a rough finished surface, and process preciseness is lowered by deflection of the grindstone. Therefore, most suitable for the finishing process of the mold is the use of a so-called ball-nose grindstone of which the tip is round.
However, the finishing process of a free surface using the ball-nose grindstone causes lowering of grinding efficiency after a short time and requires frequent dressing of the grindstone offline, because in-process dressing of the grindstone is impossible. This causes problems that are time consuming and difficult to reset the position of the grindstone resulting in low preciseness produced.
On the other hand, electrolytic in-process dressing grinding (hereafter, ELID grinding) was developed and published by the present applicants as a grinding means to achieve high efficient and ultra-precise mirror surface grinding that has been considered as impossible by conventional grinding art. In the ELID grinding, the conductive bonding part of a metal bond grindstone is dissolved by electrolytic dressing, therefore dressing and grinding are done simultaneously. The present grinding method allows efficient mirror finish for an ultra-hard material by using a metal bond grindstone having fine grains and has a characteristic capable of achieving high efficiency and ultra-preciseness.
However, the ELID grinding requires an in-process electrolytic step for the grindstone and, therefore, a space for installation of electrodes other than a working part is essential. Thus, such grindstone as the ball-nose grindstone having a small working surface of the grindstone and a peculiar shape has a problem that it is difficult to install electrodes near the working surface of the grindstone.
In order to solve these problems, the applicants of the present invention previously created "an electrolytic interval dressing grinding method" and submitted an application (Japanese Patent Gazette No. 1992-115867). In this method, as diagrammatically shown in FIG. 1, an electrode 3 is installed with a gap from the objective grinding material 1 (workpiece), an conductive grindstone 2, to which a voltage has been applied, is repeatedly moved between the workpiece 1 and the electrode 3, and a conductive grinding fluid is supplied between the conductive grindstone 2 and the workpiece 1 to carry out alternately electrolytic dressing and grinding process.
However, it is a problem that grinding by this method is inefficient and application to a peculiar grindstone such as the ball-nose grindstone is difficult, because alternation of the electrolytic dressing and grinding process is required.
Further, the applicants of the present invention created "an electrolytic dressing method and apparatus using an electrode contacting a semiconductor" and submitted an application (Japanese Patent Gazette No. 1994-170732). In this means, as diagrammatically shown in FIG. 2, a conductive grinding fluid is supplied to a gap between the conductive grindstone 2 having a contact surface to the workpiece 1 and the electrode 3 made of a semiconductor material and contacted to the working surface, a voltage is applied between the grindstone 2 and the electrode 3, and the grindstone 2 is subjected to dressing by electrolysis. For reference, 4, 5, and 6 represent a brush, an electric power source, and a nozzle.
The electrode 3 consisting of a semiconductor material allows electrolytic dressing of the grindstone by direct contact to the contacting surface (working surface) of the grindstone 2. This means also has a problem that application to a peculiar grindstone such as the ball-nose grindstone is difficult.